The lymphatic system includes a network of vessels generally separate from veins and arteries. Rather than whole blood, the lymphatic vessels carry lymphatic fluid (or lymph). The lymphatic system serves a variety of physiologic purposes, including returning interstitial fluid to the vascular space, transporting fats from the digestive tract, and transporting immune-mediating cells. The composition of lymphatic fluid is similar to plasma. It contains white blood cells, but generally does not contain red blood cells, platelets, or various other components of whole blood. The lymphatic system may be involved in a variety of pathologic states, including lymphatic obstruction leading to lymphedema, leakage of lymphatic fluid, which may lead to chylothorax, or the invasion and spread of malignant cells leading to metastasis. The lymphatic system is involved in nearly any immune mediated response, whether to infectious agents (e.g., viruses, bacteria, parasites, etc.), malignancy, or in the setting of auto-immune disorders. The lymphatic system may serve as a repository for infected cells in disorders such as HIV or may contain a higher concentration of malfunctioning cells in various immune system disorders. To achieve diagnosis and/or treatment of these and other conditions, it may be desirable to access the lymphatic system.